Microwave antenna probe having a deployable ground plane

ABSTRACT

A surgical ablation system employing an ablation probe having a deployable ground plane is disclosed. The disclosed system includes a source of ablation energy and a source of electrosurgical energy, and a switching assembly configured to select between ablation and electrosurgical modes. The probe includes a cannula having a shaft slidably disposed therein. The shaft includes a deployable ground plane electrode assembly and a needle electrode disposed at distal end of the shaft. As the shaft is extended distally from the cannula, the ground plane electrode unfolds, and the needle electrode is exposed. Electrosurgical energy is applied to tissue via the needle electrode to facilitate the insertion thereof into tissue. Ablation energy is applied to tissue via the needle electrode to achieve the desired surgical outcome. The shaft, ground plane electrode and needle electrode are retracted into the cannula, and withdrawn from the surgical site.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S. application Ser. No. 12/719,657, now U.S. Pat. No. 8,728,067, filed Mar. 8, 2010, the entire disclosure of which is incorporated by reference herein.

BACKGROUND

1. Technical Field

The present disclosure relates to systems and methods for providing energy to biological tissue and, more particularly, to a microwave ablation surgical system and probe having a deployable ground plane, and methods of use therefor.

2. Background of Related Art

Energy-based tissue treatment is well known in the art. Various types of energy (e.g., electrical, ultrasonic, microwave, cryogenic, thermal, laser, etc.) are applied to tissue to achieve a desired result. Electrosurgery is a technique of using alternating current electrical signals, using a carrier frequency in the approximately 200 kHz-3.3 MHz range, in connection with surgical instruments, to cut or coagulate biologic tissue endogenically. This electrosurgical signal can be a sinusoidal waveform operating in a continuous mode at a 100% duty cycle, or pulse modulated at a duty cycle of less than 100%. Typically, electrosurgical signals are operated at 100% duty cycle for maximal cutting effect, and are pulse modulated at duty cycles ranging from 50% to 25% for less aggressive cutting, also referred to as blending, or, at a substantially lower duty cycle of approximately 6%, for coagulating. The electrosurgical carrier signal can also be varied in intensity. The electrosurgical signal is applied to the patient via electrodes in either monopolar mode, or bipolar mode. In monopolar mode, the active electrode is the surgical instrument at the surgical site, and the return electrode is elsewhere on the patient, such that the electrosurgical signal passes through the patient's body from the surgical site to the return electrode. In bipolar mode, both the active and return electrodes are at the surgical site, effectuated by, for example, both jaw members of a pair of forceps, such that the electrosurgical signal passes through only the tissue that is held between the jaw members of the instrument.

In tissue ablation electrosurgery, electrosurgical energy (e.g., microwave, radiofrequency) may be delivered to targeted tissue by an antenna or probe. There are several types of microwave antenna assemblies in use, e.g., monopole, dipole and helical, which may be used in tissue ablation applications. In monopole and dipole antenna assemblies, microwave energy generally radiates perpendicularly away from the axis of the conductor. Monopole antenna assemblies typically include a single, elongated conductor. A typical dipole antenna assembly includes two elongated conductors, which are linearly aligned and positioned end-to-end relative to one another with an electrical insulator placed therebetween. Helical antenna assemblies include a helically-shaped conductor connected to a ground plane. Helical antenna assemblies can operate in a number of modes including normal mode (broadside), in which the field radiated by the helix is maximum in a perpendicular plane to the helix axis, and axial mode (end fire), in which maximum radiation is along the helix axis. The tuning of a helical antenna assembly may be determined, at least in part, by the physical characteristics of the helical antenna element, e.g., the helix diameter, the pitch or distance between coils of the helix, and the position of the helix in relation to the probe assembly to which it is mounted.

The typical microwave antenna has a long, thin inner conductor that extends along the longitudinal axis of the probe and is surrounded by a dielectric material and is further surrounded by an outer conductor around the dielectric material such that the outer conductor also extends along the axis of the probe. In another variation of the probe that provides for effective outward radiation of energy or heating, a portion or portions of the outer conductor can be selectively removed. This type of construction is typically referred to as a “leaky waveguide” or “leaky coaxial” antenna. Another variation on the microwave probe involves having the tip formed in a uniform spiral pattern, such as a helix, to provide the necessary configuration for effective radiation. This variation can be used to direct energy in a particular direction, e.g., perpendicular to the axis, in a forward direction (i.e., towards the distal end of the antenna), or combinations thereof.

Invasive procedures and devices have been developed in which a microwave antenna probe may be either inserted directly into a point of treatment via a normal body orifice or percutaneously inserted. Such invasive procedures and devices potentially provide better temperature control of the tissue being treated. Because of the small difference between the temperature required for denaturing malignant cells and the temperature injurious to healthy cells, a known heating pattern and predictable temperature control is important so that heating is confined to the tissue to be treated. For instance, hyperthermia treatment at the threshold temperature of about 41.5° C. generally has little effect on most malignant growth of cells. However, at slightly elevated temperatures above the approximate range of 43° C. to 45° C., thermal damage to most types of normal cells is routinely observed. Accordingly, great care must be taken not to exceed these temperatures in healthy tissue.

In the case of tissue ablation, a high radio frequency electrical current in the range of about 300 MHz to about 10 GHz is applied to a targeted tissue site to create an ablation volume, which may have a particular size and shape. Ablation volume is correlated to antenna design, antenna performance, antenna impedance and tissue impedance. The particular type of tissue ablation procedure may dictate a particular ablation volume in order to achieve a desired surgical outcome. By way of example, and without limitation, a spinal ablation procedure may call for a longer, narrower ablation volume, whereas in a prostate or liver ablation procedure, a more spherical ablation volume may be required.

In some instances, targeted lesions may be located on or near the surface of the target organ, e.g., the “dome” or top of a liver. Conventional ablation probes may radiate ablation energy into the surrounding tissue, for example, the abdominal wall. In such instances, surface lesions may treated with an invasive ablation needle having a radial ground plane that is adapted to shield adjacent tissues from undesirable exposure to ablation energy. However, such ground planes may have a diameter that is substantially greater than that of the probe shaft, which may preclude the use of laparoscopic treatment, or, require a large puncture to be created in the skin and/or adjacent anatomical structures during such non-invasive procedures. Additionally, insertion of a needle probe into dense or fibrous tissue may be difficult and place stress on the probe, which may lead to probe failure and operative complications.

SUMMARY

The present disclosure is directed to a microwave ablation probe having a deployable ground plane electrode. The disclosed microwave ablation probe includes a shaft having an inner conductor and a dielectric coaxially disposed around the inner conductor. The inner conductor extends distally beyond a distal end of the dielectric to form a needle electrode. An outer shield is coaxially disposed around the dielectric and is coupled to a deployable ground plane assembly electromechanically joined to a distal end of the dielectric. The ground plane assembly, as well as other ground plane assemblies described herein, may, when deployed, have a generally umbrella-like shape, however, it is to be understood the disclosed deployable ground planes may include any shape, including without limitation ovoid, polygonal, and a ground plane described by radial projections.

A ground plane assembly in accordance with the present disclosure may include one or more support wires extending radially from a distal end of the dielectric and/or the outer conductor. The support wires may be formed from resilient material, such as without limitation, spring steel, shape memory alloy, carbon fiber, fiberglass composite material, and the like. The support wires are arranged in a radial cantilever configuration, such that, in an embodiment, the wires extend approximately transversely to a longitudinal axis of the shaft when at rest (e.g., when the wires are in a deployed, unloaded or undeflected state).

A generally circular flexible conductive membrane is electromechanically fixed to the support wires in a generally umbrella-like fashion to form a ground plane electrode. Prior to use, the ground plane electrode may folded against the probe shaft, e.g., positioned in a stowed or undeployed configuration. The probe may be introduced into a cannula, which may have an inner diameter dimensioned to retain the folded ground plane electrode in the stowed configuration. During use, a distal end of a cannula having a described probe positioned therein, may be introduced to the surgical site. The cannula may be withdrawn and/or the probe may be advanced, causing the ground plane assembly to extend from the cannula to expose the ground plane assembly. Once free of the cannula, the biasing force of the wires causes the ground plane assembly to deploy, e.g., to fold open. The needle electrode may then be inserted into targeted tissue and a source of ablation energy activated to deliver ablation energy to targeted tissue. Electrosurgical energy (having, e.g., a cutting waveform) may be applied to tissue via the needle electrode to ease or facilitate the insertion of the needle electrode into tissue. After the needle electrode is positioned in tissue, ablation energy may then be applied to tissue to perform the desire ablation procedure.

Also disclosed is an electromagnetic surgical ablation system that includes a source of ablation energy and a source of electrosurgical energy, and a switching assembly configured to selectively apply either the source of ablation energy or the source of electrosurgical energy to an inner conductor of an ablation probe. The disclosed system includes an ablation probe comprising a generally tubular cannula having a proximal end and a distal end, and a shaft slidably disposed within the cannula and having at least a stowed position and a deployed position. The shaft includes an inner conductor adapted to operably couple to the switching assembly. The inner conductor may be coaxially disposed within the shaft, and may extend from a distal end thereof to form a needle electrode. The probe includes a deployable ground plane electrode assembly disposed about a distal end of the shaft, wherein, when the shaft is in a stowed position the deployable ground plane electrode is substantially folded within the cannula, and when the shaft is in a deployed position the deployable ground plane electrode extends substantially radially from a distal end of the shaft.

A method of using a surgical ablation system is presented herein, comprising the steps of positioning an ablation probe at an operative site, wherein the ablation probe includes a cannula having therein a deployable ground plane antenna and a distal needle electrode. The ground plane antenna and distal needle electrode are deployed (e.g., extended from the cannula). Electrosurgical energy may be delivered to tissue via the needle electrode to facilitate the insertion of the needle electrode into tissue, and the needle electrode is inserted into tissue. After the needle is inserted into tissue, ablation energy may be delivered to tissue via the needle electrode. After the ablation is complete, the needle electrode is withdrawn from tissue, the ground plane antenna is retracted into the cannula, and the ablation probe is removed from the operative site. The disclosed method may additionally include the step of insufflating the operative site with a gas, such as carbon dioxide, to form a pneumoperitoneum.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic representation of a microwave ablation system that includes an ablation probe having a deployable ground plane in accordance with the present disclosure;

FIG. 2 is a side, cutaway view of an embodiment of a microwave ablation probe having a deployable ground plane in accordance with the present disclosure

FIG. 3 is a side, partial cutaway view of an embodiment of a microwave ablation probe having a deployable ground plane, in a first position, in accordance with the present disclosure;

FIG. 4 is a side, partial cutaway view of an embodiment of a microwave ablation probe having a deployable ground plane, in a second position, in accordance with the present disclosure;

FIG. 5 is a side, partial cutaway view of an embodiment of a microwave ablation probe having a deployable ground plane, in a third position, in accordance with the present disclosure;

FIG. 6 is a side, partial cutaway view of an embodiment of a microwave ablation probe having a deployable ground plane, in a fourth position, in accordance with the present disclosure;

FIG. 7 is distal end view of an embodiment of a microwave ablation probe having a deployable ground plane in accordance with the present disclosure;

FIG. 7A is edge, cross sectional view of an embodiment of ground plane assembly in accordance with the present disclosure;

FIG. 8 is distal end view of another embodiment of a microwave ablation probe having a deployable ground plane in accordance with the present disclosure;

FIG. 9 is distal end view of yet another embodiment of a microwave ablation probe having a deployable ground plane in accordance with the present disclosure;

FIG. 10 is distal end view of still another embodiment of a microwave ablation probe having a deployable ground plane in accordance with the present disclosure;

FIG. 10A is a perspective view of the FIG. 10 embodiment of a microwave ablation probe having a deployable ground plane assembly in a closed position, in accordance with the present disclosure;

FIG. 10B is a perspective view of the FIG. 10 embodiment of a microwave ablation probe having a deployable ground plane assembly in an open position, in accordance with the present disclosure;

FIG. 11 is distal end view of a further embodiment of a microwave ablation probe having a deployable ground plane in accordance with the present disclosure;

FIGS. 12A-12J illustrate a method of use of a microwave ablation probe having a deployable ground plane in accordance with the present disclosure;

FIG. 13A illustrates an embodiment of a ground plane leaf having a conductive element disposed thereupon in accordance with the present disclosure; and

FIG. 13B illustrates another embodiment of a ground plane leaf having a conductive element disposed thereupon in accordance with the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure are described hereinbelow with reference to the accompanying drawings; however, it is to be understood that the disclosed embodiments are merely exemplary of the disclosure, which may be embodied in various forms. Well-known and/or repetitive functions and constructions are not described in detail to avoid obscuring the present disclosure in unnecessary or redundant detail. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure in virtually any appropriately detailed structure. In addition, as used herein, the term “proximal” shall refer to the end of the instrument that is closer to the user, while the term “distal” shall refer to the end that is farther from the user, as is customary.

FIG. 1 shows an embodiment of a microwave ablation system 10 in accordance with the present disclosure. The microwave ablation system 10 includes an electromagnetic surgical ablation probe 5 operatively coupled by a cable 15 to connector 16, which may further operably couple the antenna probe 10 to a selector switch 22, which, in turn, selectively and operably couples an ablation generator assembly 20 and/or an electrosurgical generator assembly 18 to probe 10. Switch 22 may be any suitable switching device, including without limitation a mechanical switch, relay, semiconductor, and/or combinations thereof. Ablation generator 20, electrosurgical generator 18, and/or switch 22 may be operably coupled to a controller 24. Probe 10 includes a distal radiating portion 11 having a generally shallow umbrella-shaped ground plane 12 disposed thereupon. As depicted in FIG. 1, ground plane 12 is in a deployed position. A needle electrode 13 extends distally from the probe 10, which is also depicted in FIG. 1 in a deployed position. Ablation generator assembly 20 is a source of ablation energy, e.g., microwave or RF energy in a range of about 300 MHz to about 10 GHz. In embodiments, generator assembly 20 may provide ablation energy in a range of about 915 MHz to about 2.45 GHz. Electrosurgical generator 18 is a source of electrosurgical energy in a range of about 200 kHz to 3.3 MHz range and configured to provide one or more electrosurgical waveforms adapted to facilitate cutting, coagulating, blending, etc. Electrosurgical generator 18 may include a return electrode input (not explicitly shown) to accommodate a return electrode pad that is used during monopolar electrosurgical procedures.

With reference to FIGS. 2 and 3, a coaxial fed microwave ablation probe 100 is shown. The disclosed probe 100 includes a shaft assembly 110 slidably disposed within a cannula 112. The shaft 110 includes an inner conductor 101 disposed coaxially within dielectric 102, and an outer conductor 103 coaxially disposed around the dielectric 102. The inner conductor 101 extends distally from the dielectric 102 to form a needle electrode 104, which may include a sharpened distal tip 105 to ease the insertion thereof into tissue. As shown in FIGS. 2 and 3, distal tip is substantially aligned with a distal end 113 of trocar 112.

Shaft 110 includes an umbrella-like deployable ground plane electrode assembly 120 disposed generally at a distal end 106 of dielectric 102. The umbrella-like deployable ground plane assembly 120 includes a plurality of wire elements 121, each having a fixed end 123 and a free end 124. The umbrella-like deployable ground plane 120 assembly is movable between a stowed position, as seen generally in FIGS. 2 and 3, and a deployed position as seen in FIG. 6. The wire elements may be formed from any suitable resilient material having sufficient flexibility to be stowed in a first position while having sufficient elasticity to recover to a deployed position as shown in FIG. 6. For example, and without limitation, wire elements 121 may be formed from shape memory alloy (e.g., nitinol), stainless steel, platinum, or other material exhibiting similar elastic and recovery characteristics.

A fixed end 123 of each wire element 121 may be fixed to a distal end 106 of dielectric 102 such that, in a deployed position, a wire element 121 extends substantially radially from (orthogonal to) shaft 110. Fixed end 123 of wire element 121 may be joined to dielectric 102 by any suitable manner of connection, including without limitation by mechanical and/or interference fit into a corresponding opening (not explicitly shown) defined within dielectric 102, and/or by soldering, welding, brazing, adhesive coupling, and the like. Additionally or alternatively, a fixed end 123 of each wire element 121 may be fixed to a distal end of outer conductor 103 and operably electrically coupled thereto.

A flexible ground plane membrane 122 is disposed in electrical communication onto the plurality of wire elements 121 of umbrella-like deployable ground plane assembly 120. Ground plane membrane 122 may be formed from any electrically conductive material having sufficient flexibility, strength and heat resistance to enable the deployment and/or retrieval of ground plane assembly 120, such as, without limitation, metallic foil, metallic mesh, and/or metal-coated polymers, e.g., aluminized biaxially-oriented polyethylene terephthalate (a.k.a., boPET or Mylar™).

In a stowed or closed position, best illustrated in FIGS. 2 and 3, the ground plane assembly 120 is folded such that free ends 124 of wire elements 121 may be positioned substantially adjacent to or in contact with shaft 110 at a location proximal of a distal end of dielectric 102. An outward, or opening, bias of the wire elements 121 is resisted by the cannula 112 to confine ground plane assembly 120 to a stowed position. Ground plane assembly 120 may be moved to a deployed position as seen in FIGS. 4-6 by advancing the shaft 110 distally in relation to cannula 112, and/or, withdrawing cannula 112 proximally with respect to shaft 110.

As seen in FIG. 4, shaft 110 has been moved distally with respect to cannula 112, thereby exposing a distal portion of ground plane assembly 120. An inner surface of cannula 112 may include a lubricious coating, such as without limitation, polytetrafluoroethylene (PTFE) (e.g., Teflon®, manufactured by E. I. du Pont de Nemours and Company of Wilmington, Del., United States), which may facilitate movement of shaft 110 and/or ground plane assembly 120 within cannula 112. As shown in FIG. 4, a proximal portion (e.g., the free ends 124) of closed ground plane assembly 120 remains within cannula 112, thereby retaining ground plane antenna 120 in a closed position. Turning now to FIG. 5, shaft 110 is moved further distally, moving ground plane assembly 120 clear of cannula 112 and thus enabling wire elements 121 to recover to a relaxed position, which causes ground plane 120 to open into a deployed position best seen in FIGS. 6 and 7. It is envisioned that the deployment of ground plane assembly 120 (once clear of cannula 112) may occur in a generally instantaneous motion or in a gradual motion. In embodiments, the deployment time of ground plane assembly 120 may range from less than 50 milliseconds to about five seconds.

Ground plane assembly 120 may include a dielectric coating on a surface thereof, e.g., a distal surface, a proximal surface, or an edge thereof (as referenced to a ground plane assembly in an open or deployed position). Additionally or alternatively, ground plane membrane 122 may include a plurality of layers and/or laminations, as shown in FIG. 7A. In one envisioned embodiment, at least one inner surface 125 between layer 122 a and 122 b includes a metallic coating. An outer surface 126 a and/or 126 b includes a dielectric coating. It is also envisioned that a layer 122 a and/or 122 b may be formed from a dielectric material, such as without limitation PTFE, or boPET (e.g., Mylar®, manufactured by E. I. du Pont de Nemours and Company of Wilmington, Del., United States).

Additional envisioned embodiments of a ground plane assembly in accordance with the present disclosure are discussed with reference to FIGS. 8-11. As seen in FIG. 8, a ground plane assembly includes one or more leaf-like ground plane elements 224 radially disposed about a dielectric distal end 206. Each ground plane element 224 includes a wire element 221 having two fixed ends 223 that are operably fixed to a dielectric distal end 206 as described hereinabove to form a petal-like wire loop 225. A ground plane membrane 222 is disposed upon each wire loop 225 to form a ground plane element 224. Each ground plane element may be stowed within a cannula (not explicitly shown) in a closed position, and deployed at an operative site into an open position as described herein.

In FIG. 9, an alternative ground plane assembly 240 is depicted wherein one or more ground plane elements 224 are disposed in an asymmetrical radial arrangement. Such an asymmetrical arrangement may provide alternative ablation patterns which may be desirable in particular surgical scenarios, e.g., wherein irregularly-shaped or asymmetrical tumors or lesions are targeted. In an embodiment, wire element 241 may include a score (not explicitly shown) at a juncture 243 where wire element 241 is joined to dielectric distal end 207. A user (e.g., a surgeon) may tailor a ground plane assembly 240 by bending unwanted ground plane elements 244 at the score until the wire element 241 breaks, thus enabling the removal of individual ground plane elements 244 from the ground plane assembly 240. In this manner, the ablation pattern and/or physical dimensions of the ground plane assembly and probe associated therewith may be adapted to the particular requirements of a surgical procedure.

Yet another embodiment is described herein with reference to FIGS. 10, 10A, and 10B, wherein a microwave ablation probe 300 includes a ground plane assembly 320 having one or more deployable ground plane leaves 322 disposed in a radial arrangement to a dielectric distal end 306 of probe 300. Leaves 322 may be formed from resilient substrate material, e.g., shape memory alloy sheet material, shape memory polymeric sheet material, and/or resilient polymeric sheet material, such as without limitation, polyimide, e.g., Kapton™ film manufactured by E. I. du Pont de Nemours and Company of Wilmington, Del., United States. Leaves 322 may have a laminated construction, wherein in an embodiment, a substrate material may include a dielectric coating on an outer surface thereupon to form an insulating layer between a substrate material and tissue. In yet another embodiment illustrated in FIG. 13A, a leaf 360 may be formed from a nonmetallic substrate 361, which may include one or more conductive elements 362 disposed thereupon having a substantially solid pattern. As seen in FIG. 13B, a leaf 370 may include one or more conductive elements 372 (e.g., circuit traces) arranged in a generally serpentine pattern, which may enhance or control ablation volumes. A contact region 363, 373 may additionally or alternatively be included to facilitate electrical and/or mechanical coupling of a leaf 360, 370 to an associated probe (e.g., a dielectric and/or outer conductor thereof). The disclosed conductive elements may provide a ground plane electrode and/or may be formed from resistance metal, e.g., nickel-chromium resistance metal (a.k.a. nichrome), through which an electric current may be passed. The electric current causes heating of the resistance metal which, in turn, causes heating of a shape memory substrate layer associated therewith, to activate shape memory material transformation to facilitate deployment of the ground plane electrode.

In a further embodiment illustrated in FIG. 11, a ground plane assembly 340 includes one or more leaves 341-348 of varying shapes and/or sizes, which may improve or control an ablation pattern of a ground plane assembly and/or an associated probe, and which may tailor ablation performance to particular requirements of a surgical procedure.

Turning now to FIGS. 12A-12J, a method of use of a microwave ablation probe having a deployable ground plane in accordance with the present disclosure is described. With reference to FIGS. 12A and 12B, the disclosed method includes the steps of providing to targeted tissue T at a surgical site a cannula 401 having stowed therein an ablation probe 402 that includes a deployable ground plane electrode 403 and a needle electrode 404. As seen in FIGS. 12B and 12C, the cannula 401 is retracted relative to the probe 402 to expose the deployable ground plane 403. Additionally or alternatively, the probe 402 may be advanced with respect to the cannula 401 and/or targeted tissue T. As the retraction of cannula 401 and/or the advancement of probe 402 proceeds, deployable ground plane 403 is exposed completely causing the deployment thereof into an open position as shown in FIGS. 12D and 12E.

The probe 402, and optionally the cannula 401, are advanced toward the targeted tissue T thereby inserting needle electrode 404 into the targeted tissue and/or bringing ground plane 403 into contact with a surface thereof as shown in FIG. 12F. Electrosurgical energy may be applied via needle electrode 404 to facilitate the insertion thereof into targeted tissue T. Probe 402 is then energized to deliver ablation energy to tissue T via, e.g., needle electrode 404. The probe 402 is then retracted and needle electrode 404 removed from tissue T as shown in FIG. 12G. Probe 402 continues to be retracted into cannula 401, causing ground plane 403 to fold forward, and slide into cannula 401 as depicted in FIGS. 12H and 12I. Cannula 401 is then withdrawn from tissue T as shown in FIG. 12J.

It is envisioned the steps of the above method may be performed in a different order than that described, and/or the operations performed within an individual step or steps may be desirably be combined into a single step without departing from the scope and spirit of the method disclosed herein. For example, and without limitation, needle electrode 404 may be inserted into targeted tissue prior to deployment of ground plane 403, which may result in ground plane 403 to contact tissue T substantially immediately upon deployment. In another example, and without limitation, once probe 402 is retracted into cannula 401, causing ground plane 403 to fold forward, as depicted in FIGS. 12H, 12I, and 12J, subsequent retraction of cannula 401 relative to probe 402 results in the free end of ground plane 403 to be exposed from cannula 401 prior to the fixed end of ground plane 403.

The described embodiments of the present disclosure are intended to be illustrative rather than restrictive, and are not intended to represent every embodiment of the present disclosure. Further variations of the above-disclosed embodiments and other features and functions, or alternatives thereof, may be made or desirably combined into many other different systems or applications without departing from the spirit or scope of the disclosure as set forth in the following claims both literally and in equivalents recognized in law. 

What is claimed is:
 1. A surgical ablation probe, comprising: a cannula having a distal end and defining a longitudinal axis; a shaft disposed within the cannula and being movable along the longitudinal axis and relative to the cannula between a stowed position and a deployed position; an inner conductor disposed within the shaft, the inner conductor including a distal portion; a needle electrode electrically coupled to the distal end of the inner conductor; and a deployable ground plane assembly coupled to the distal end of the shaft and disposed within the cannula when the shaft is in the stowed position, wherein when the shaft is moved from the stowed position to the deployed position, the distal portion of the inner conductor and the deployable ground plane assembly extend past the distal end of the cannula thereby expanding deployable ground plane assembly radially from the distal end of the shaft.
 2. The surgical ablation probe according to claim 1, wherein the shaft includes an outer conductor coaxially disposed over the inner conductor.
 3. The surgical ablation probe according to claim 2, wherein the distal portion of the inner conductor extends past a distal end of the outer conductor.
 4. The surgical ablation probe according to claim 2, wherein the deployable ground plane assembly is electrically coupled to the outer conductor.
 5. The surgical ablation probe according to claim 1, wherein the deployable ground plane includes a plurality of ground plane elements.
 6. The surgical ablation probe according to claim 5, wherein each of the plurality of ground plane elements includes a respective one of a plurality of resilient wires.
 7. The surgical ablation probe according to claim 6, wherein the plurality of resilient wires bias the deployable ground plane assembly radially outward from the shaft.
 8. The surgical ablation probe according to claim 7, wherein each of the plurality of resilient wires includes a first end fixed to the distal end of the shaft and a free end, and the deployable ground plane assembly includes a flexible ground plane membrane disposed over the plurality of resilient wires.
 9. The surgical ablation probe according to claim 8, wherein the deployable ground plane electrode assembly includes a flexible ground plane membrane disposed over the plurality of resilient wires.
 10. The surgical ablation probe according to claim 7, wherein each of the plurality of resilient wires forms a loop, each one of the plurality of loops having a first end and a second end each fixed to the distal end of the shaft, and the deployable ground plane electrode assembly further includes a plurality of flexible ground plane membranes disposed over a respective one of the plurality of loops.
 11. A method of using a surgical ablation system, comprising: positioning an ablation probe at an operative site, wherein the ablation probe includes: a cannula having a distal end and defining a longitudinal axis; a shaft disposed within the cannula and being movable along the longitudinal axis and relative to the cannula between a stowed position and a deployed position; an inner conductor disposed within the shaft, the inner conductor including a distal portion; a needle electrode electrically coupled to the distal end of the inner conductor; and a deployable ground plane assembly coupled to the distal end of the shaft and disposed within the cannula when the shaft is in the stowed position; deploying the shaft from the stowed position to the deployed position, such that the distal portion and the deployable ground plane assembly extend past the distal end of the cannula and the deployable ground plane assembly expands radially from the distal end of the shaft; inserting the distal portion into tissue; and delivering ablative energy to the tissue through the distal portion of the inner conductor and the deployable ground plane assembly.
 12. The method according to claim 11, wherein the distal portion of the inner conductor extends past a distal end of the outer conductor.
 13. The method according to claim 12, wherein inserting the distal portion of the inner conductor into the tissue further includes delivering electrosurgical energy to the tissue through the distal portion of the inner conductor.
 14. The method according to claim 12, further comprising switching between delivery of the electrosurgical energy and delivery of the ablative energy. 